Radio frequency display sign



I n R m l m. 2, w R 5 3 WW mm M. 2 Z. Z v s i v H a K n N B "M F R Y m M 6 3 4 s A "w a w. u H a 2 M M aa 2%23 l? E m m LT M. W. /Ll F O I] April 14, 1953 Flled Feb 26, 1949 April 14, 1953 r- M. SHOEMAKER 2,635,215

RADIO FREQUENCY DISPLAY sxcu Filed Feb; 26, 1949 2 SHEETS--SHEET 2 Patented Apr. 14, 1953 RADIO FREQUENCY DISPLAY SIGN Frank M. Shoemaker, Pittsburgh, Pa.

Application February 26, 1949, Serial No. 78,655

3 Claims.

This invention relates generally to high frequency energized signs or displays and more particularly to a sign or display free of radio and. video interference.

High frequency energized signs and displays, employing direct connected'or capacity coupling to illuminate the characters, produce an interference detrimental to both radio and video reception. In fact instances have occurred wherein such high frequency energized signs have actually jammed commercial and. governmental communications. Again parts of such circuits must be carefully insulated to prevent accidental injury owing to the proximity and the personal interest that such signs and displays are purposely intended, although the illuminated characters may themselves be handled in the proximity of the capacity coupling without injury. The circuits generally employed to energize capacity coupled signs or displays invariably have a low Q which is conducive to high radiation of interfering harmonics whether the frequency generated is below that of broadcast band or is within the video band.

The principal object and advantage of this invention is the provision of l a high frequency sign or display wherein the characters are energized by a circuit operating on a fixed selected frequency through a capacity coupling that is 'not dangerous and provides a high Q circuit that is substantially nil of interference radiation by the elimination of harmonics. This type of ci r cult permits the choice of an oscillating frequency that is lower than the frequency used in the present capacity. coupled high frequency signs and displays, which fact obviously results in a materially less radiation at the selected fundamental frequency.

This invention also contemplates a novel oscillating circuit wherein the plate and load circuits are tuned and the grid circuit is not tuned, although all three parts of the circuit are inductively coupled.

Another object is the provision of an oscillatory circuit employing a high frequency transformer the secondary of which provides the inductance of a closed resonant circuit which is the load circuit and the capacity of which is low and resonates at a selected low frequency of the same order as in the resonant plate circuit, permitting the latter to function with a high Q.

One of the principal distinctions between the novel circuit comprising this invention and that of other oscillating circuits resides in the fact that the pres t ci cuit has a tuned and resonated plate circuit-that is required to produce resonance at a selected low frequency in the load circuit. The use of a low capacity in the resonant load circuit permits the construction of a very simple and economical unshielded capacitive load mat for use in providing the capacity coupling from the resonant load circuit to the gas filled or fluorescent treated characters without radiating interference. energy.

Other objects and advantages appear hereinafter in the following description and claims.

The accompanying drawings show, for the purpose of exemplification but without limiting the invention or claims thereto, certain practical embodiments of the invention wherein:

Fig. 1 is a circuit diagram comprising this invention wherein the power supply is connected as a shunt feed to the oscillating circuit employing a triode with a radio frequency transformer coupling between the resonant plate circuit and the resonant load circuit.

Fig. 2 is a circuit diagram similar to that of Fig. 1 except the'power supply is connected as a series feed to the oscillating circuit employing a pentode,

Fig. 3 is a similar circuit diagram using a shunt fed oscillating circuit employing an autotype radio frequency transformer coupling between the resonant plate circuit and the resonant load circuit.

" Fig. 4 is a similar circuit diagram using a series fed oscillating circuit employing an autotype radio frequency transformer coupling between the resonant plate circuit and the resonant load circuit.

Fig. 5 is a plan view of the capacitive coupled load mat with some characters indicated there- Fig. 6 is a sectional view of the capacitive coupled load mat shown in Fig. 5.

7 Referring principally to Fig. l of the drawing, the vacuum tube l is a triode having the anode Z, the control grid 3, and the indirectly heated cathode 4, the heater of which is not shown. The cathode 4 is connected by wire 5 to the grid blocking resistor 6 and the switch I connected in multiple, the other side of which is connected to ground and the negative polarity of a suitable source. of high voltage D. C. supply by the wire 8. The positive polarity of the high voltage D. C. supply is connected by the wire ill to the R. F. by-pass condenser H and the R. F. choke l2. Theother side of the condenser H is connected to' ground for the purpose of by-passing the power supply with any radio frequency that may get through the R. F. choke coil !2. The other end of the coil I2 is connected by the wire l3 to the anode 2 and to the D. C. blocking condenser I l. The other side of the blocking condenser M is connected by the wire I5 to the anode tank circuit made up of the inductance l6 and the capacitance I! which form the plate resonant circuit which must be turned to a selected frequency such as 120 kc. The other side. of this plate resonant circuit is connected by 18 to ground.

The grid 3 is connected through the wire .20 to the antiparasitic resistor 2|, the other end of which is connected by the wire'22 to one end;of the pickup coil 23 that is in turn connected by 24 to the grid leak condenser 25 and the 'gridlea-k resistor 23 that are connected in multiple'and to the Wire 8 that is rounded.

The resonant load circuit consists of the inductance 27 and the capacitance 28, the former having materially more turns and functioning in the manner as a secondary relativeto theinductance I6 which functions as a primary ofna radio frequency transformer .and'has materially iess number of turns.

One side of the capacitance ZB-of the resonate load circuit is connected by the wires: l8 and 29 to ground and to 'one end of the inductance .21, the other end of these resonant elements areconnected together by the wire 30.

It is preferable to place each of the inductances I6, 21 and the pickup23 inalignment on alsingle form as indicated by their-arrangement in the circuit diagram.

The capacitance .28 lSIlllCfiECtifiIlllIiShlldGd load mat as illustrated in-Figs..;5':andf6 wherein one side oftthe'capacity. is formedby'a series-of electrodes 3|, 32 and 33 connected at one end by the strip 34: and theother'side .isformed by the series of electrodes :35, Miami 31 connected at the other end of the mat 28*bythestrips38. The leads 29 and 30may-beiconnected to therespective sides of the capacitancemat at any desired location.

In constructing the mat 28 itxhas-been-determined preferable toremploy; aluminum foil for the strips which areinterposed as'a stratified layer in the plastic board was shownxin Figs. 5 and 6. The plastic. making up the board may be of any suitable opaque thermosetting' phenol formaldehyde resin or a clear thermoplastic resin such as methyl methacrylate. The. latter. matwill of course show the'foil; strips but thecardinal parts of the characters may be discerned from either side of the board. Themating pairsof strips should be placed toprovide a "properly spaced electrostatic field: suitable for thesize or dimension of the characters to be employed. The characters as indicated at may be-sealedtubes having an innercoating of fluorescent material and supplied with ionizable gas suchas mercury vapor, or they may be made of-a fritted glass containing fluorescent material and anionizable gas wherein the fritted glass maybe molded into a suitable character.

These characters may beplaced onthe shelves A2 and rest back against .thesurface of. the mat to. The shelves hold the characters so that they are properly spaced relative to the corresponding pairsof strips3l and 35 and the electrostatic field will ionize thegas which inturn causes the fluorescent material to-glow andproduce illumination. The other shelves 42 are likewise arranged to support characters relative to the other two pairs of electrodes 32. 36 and 33,

31. Again this mat may be constructed in different shapes or arranged to support characters of different forms than those indicated.

Referring to Fig. 2 which shows the power supply connected as a series feed to the circuit, the positive polarity of the high voltage D. C. supply is connected by the wire 43 to the by-pass condenser II, the other side of which is groundedto the screen grid 44.,.and to. the anode tank circuit. made up-of the inductance 45 and the capacitance 43 which are selected to form the plate resonate circuit that is likewise tuned to a selected supersonic frequency such as kc. The

other side of-this resonate circuit is connected by the wire ll to the anode 48 of the pentode 50. The cathode 51 of this pentode is connected by the wire 5. through the cathode keying circuit of the grid blocking resistor 6 and the switch 1 as previously described. The grid 52 is likewise connected by the wire 20 to the same type of gridalci'rcuit previously described. The: resonant plate'tank: circuit 45,. is not connected directly to the resonant load circuit. 2?, -28 as 3 high voltage exists between the primary inductance 45' and the'secondary inductance 21 but they are preferablywound on the same form and are sufficiently closely arranged to be inductively coupled-without causingthe resonant plate cir-.

circuit'from' arcingto the resonant load circuit. In the circuit ofFig. 3 a shunt feed is used to supply an oscillatingcircuit employing anR. F.

:autotype transformer coupling'between the resot-nant plate circuit .andthe resonant. load circuit usingthe triode I. .Thepositive polarity of the high voltage D. ,0. supply is connected by the wire In to'thezRhF. by -pass condenser. H and 57 and one. side of the capacitance 28 to ground.

The othersideof the latter is connected by the wire 53 to theother. end oftheinductance 56. Thus theresonant tankcircuit and theresonant load circuitboth include the inductancesec-tion '55 in ,theircircuits whichhasthe effect ofreducing the currentinthis section as the currents of these two resonatingcircuits flow in op- ,posite directionsandthuscancel. each other in accordance with their respective magnitude.

The circuit of Fig. 4 isaseries fed oscillating circuit employing .an R. autotype transformer coupling between the. resonant plate circuit .and the resonant load circuit using the triode l. The cathode and grid circuits are the same as that of Figs. 1-3and the positive polarity of the high voltage D. Q supply is connected by the wirelfl' to the R. F. by-pass condenserv l l, which isgrounded on its other side, and one side of theplate tank circuit formed by the capacitance'fin and that portion 55 of the .inductance 54. .The otherside of the resonant .platecircuitis connected tojthe anode} by the wire. 61. .In all other respects the circuit is made as that shown in Fig. 3.

:One particularobiect andadvantage inusing an autotype .R. transformer .couplingbetween the resonant plate tank ;circuit and resonant load inthe fact that material efhciency will be gained if the capacitance 28 is required to be materially increased, the autotransformer tap may be changed to materially increase the inductance 55 without much change in the total inductance of the whole winding 54. The higher the percentage of the inductance 55 of the total inductance 5c the higher the efficiency of the circuit in maintaining resonance in the plate and load circuits.

The cathode keying circuit formed by the grid blocking resistor 6 and its shunting switch I when opened provides a means for inserting the blocking resistor in the cathode circuit to im press a high negative voltage on the grid and thus prevent the tube from oscillating and leave the characters dark. By intermittently operating the switch I the display sign will be caused to flash.

In their operation each of these four circuits is preferably supplied with a high voltage D. C. that operates the tube on the desirable portion of its characteristic curve and upon an initial pulse creates an oscillation in the resonant plate circuit. The field of this oscillation is induced into the secondary or resonant load circuit which is of the same order as that of the primary or resonant plate circuit. In turn the pickup coil of the grid circuit has induced thereon an oscillation of correct phase and magnitude from the resonant load circuit. The measure of the inductance and capacitance of these resonant circuits is preferably inverse to each other which through feed-back is effective on the control grid to sustain the oscillations in resonant circuits.

The addition or subtraction of the characters to the mat 28 in effect change the load of the resonant load circuit which in turn changes its resonant frequency. This change in frequency is reflected through the grid pick coil to maintain the oscillations of the resonant plate circuit in the correct phase and magnitude of the new frequency in the resonant load circuit.

Thus the operating eiliciency of the circuit remains substantially unchanged regardless of the change in load of the resonant load circuit. This is one of the important objects of this invention as other types of oscillating circuits must necessarily be returned precisely to suit the load changes.

The principal difference between the present circuit and that of other oscillating circuits resides in the fact that the present circuit requires a tuned or resonant plate circuit and an inductively connected load circuit that is tuned or resonated to the same frequency as that of the resonated plate, and an untuned feed back circuit. Any change in the load is effective in changing the oscillating frequency of the plate and load circuits without materially affecting the resonances of the load circuit. On the other hand the efficiency of operation of the display signs depends upon the automatic change of the 'frequency through the feed back when the load of the resonant load circuit is changed by adding or taking away letters. This is an undesirable characteristic in other types of oscillating circuits.

By selecting a tuned or resonant plate circuit for oscillating at a frequency less than the physical dimension of the electrodes in the mat 28 the circuit will not produce a standing wave in the mat, which in itself materially reduces radiation of the resonant load frequency.

Again by selecting an oscillating frequency of alow order in-the resonantplate and load circuits the capacitance of the resonant plate circuit may be made very large incapacity, which provides a low number of turns and consequently low resistance of the inductance in the resonant plate circuit, resulting in a high Q tank circuit which is substantially devoid of harmonics and which avoids transmitting harmonics to the resonant load circuit. When the harmonics are substantially nil in the'plate and load resonant circuits there will be practically no harmonic radiation.

Although the voltage across the electrodes in the mat of the resonant load circuit is high, direct contact across these electrodesby persons merely provides suificient load, causing the 0scillationsin the resonant plate and load circuits to die down, thus almost instantly reducing the voltage to zero. Such conditions make this circuit safe for use in places where individuals can handle the display sign without danger, which is also an important object of this invention.

I claim:

1. A display device comprising an electron discharge oscillation generator having an anode, a cathode, and a control grid, 2. radio frequency step-up transformer including a primary, a secondary and a tertiary winding mounted axially in the order named to provide an efficient low frequency inductive coupling between adjacent windings with the secondary effective in shielding the tertiary winding from the primary winding to prevent high frequency coupling, a resonated anode circuit including said primary, a capacitance sign mat made up of insulating -mounted conductors spaced to produce a predetermined capacity and connected with said secondary to produce a resonated load circuit, said resonated anode circuit being tuned to a frequency of the order of said mat and secondary forming said resonated load circuit, a feed back grid circuit including said tertiary winding in an untuned circuit, and sign characters in the form of envelopes containing an ioniziable gas at low pressure coupled with said capacitance mat to illuminate the same when the circuit is enerized.

2. A display device comprising an electron discharge oscillation generator having an anode, a cathode, and a control grid, a radio frequency step-up auto-connected transformer including a primary, a secondary and a tertiary winding with one end of the primary connected to one end of the secondary and mounted axially in the order named to provide an efiicient low frequency inductive coupling between adjacent windings with the secondary effective in shielding the tertiary winding from the primary winding to prevent high frequency coupling, a resonated anode circuit including said primary, a capacitance sign mat made up of insulating mounted conductors spaced to produce a predetermined capacity and connected with said secondary to produce a resonated load circuit, said resonated anode circuit being tuned to a frequency of the order of said mat and secondary forming said resonated load circuit, a feed back grid circuit including said tertiary winding in an untuned circuit and sign characters in the form of envelopes containing an ionizable gas at low pressure coupled with said capacitance mat to illuminate the same when the circuit is energized.

3. A display device comprising an electron discharge oscillation generator having an anode, a cathode, and a control grid, a radio frequency 7, step-uptransformer"including aprimary, a secondary anda'tertia'ry Winding mounted axiallyin the order'named to rovide an efiicientlow frequency inductive coupling between adjacent windings with the=secondary efiective in shielding the tertiary winding from the primary winding to prevent high frequency coupling, a resonated anode circuit including said primary, a capacitance signm'at made of insulating mounted conductors spaced to produce a predetermined capacity and connected with said secondary to produce a resonated load circuit, said resonated anode circuit being tuned to anfrequencyof the crderof said mat and secondary forming said resonated load circuit, afeed back grid circuit including said tertiary winding in an untuned circuit, sign characters in'the form of envelopes containing-an. ionizable gas at low. pressures coupled with saidmat toilluminate when thecircuit is energized, andan intermittently operated cathode keying circuit to impress a high negative voltage on the grid circuit to suspend operation of said resonated, load circuit and flashsaid characters.

FRANK M. SHOEMAKER.

References Cited in the file of this patent UNITED STATES PATENTS 

